This invention relates to telephone systems and, in particular, to telephone systems which offer voice message services for their subscribers.
Many telephone systems now include voice message services which can be subscribed to by the telephone subscriber locations served by the system. In these telephone systems, a voice message system can be accessed via the central office switch serving the subscriber locations. Communication between the switch and the subscriber locations is over analog or digital lines to the subscriber locations. These lines may be connected by direct metallic path to the switch or through subscriber loop carriers.
For subscriber locations utilizing the voice message service, the voice message system acts to record unanswered calls to the locations. These calls can then be accessed later by the subscriber locations. The voice message system communicates with the central office switch over so-called "simplified message desk interface" links. Via these links, the voice message system transmits message waiting indicator requests and message completion requests to the switch.
The message waiting indicator requests identify the telephone numbers of the subscriber locations having recorded messages at the voice message system. These requests instruct the switch to send stutter dial tone to the subscriber locations when the subscriber locations go off-hook. The stutter dial tone provides an audible indication that a voice message is waiting.
A subscriber location can then access the voice message system over its established voice path and any waiting message can be transmitted by the voice message system to the subscriber location. After the subscriber accesses the voice message system, the voice message system sends a completion request to the switch, instructing it to discontinue sending stutter dial tone and to now send normal dial tone to the subscriber location when it goes off-hook.
As can be appreciated, in the above telephone system, the necessity for the subscriber location to go off-hook in order to be made aware of waiting messages requires frequent monitoring by the subscriber location. This limits the attractiveness of the voice message service as compared to other voice message systems, such as, for example, answering machines, which include visual indicators, e.g., lamps, which provide a ready visual indication that a message is waiting.
It is, therefore, an object of the present invention to provide a telephone system and method of the above-type in which a visual indication that there are voice messages waiting on a voice message system can be established at a subscriber location.
It is a further object of the present invention to provide a telephone system and method of the above-type in which a visual indication that there are voice messages waiting on a voice message system can be established using existing systems and with a minimal disturbance at the subscriber location.